Freethought & Rationalism Archive

pug846 · 09-04-2002, 07:58 PM

Forgive my ignorance, but how did menopause, evolve? It doesn�t seem that something that comes along so late in life would be susceptible to selection pressures. I�m also under the impression that humans are the only animals that go through something like menopause. Is there any reason for this? Why did it come into play so late in our evolutionary history?

[ September 04, 2002: Message edited by: pug846 ]</p>

Max Bane · 09-04-2002, 08:03 PM

Argh, his edit was too fast for me.

[ September 04, 2002: Message edited by: Max Bane ]</p>

pug846 · 09-04-2002, 08:06 PM

Quote:

Originally posted by Max Bane:
<strong>Argh, his edit was too fast for me.

[ September 04, 2002: Message edited by: Max Bane ]</strong>

I don't know what you're talking about...(If you talk, I'll find you and hurt you...I'm lucky I know what menopause is, let alone how to spell it.)

RufusAtticus · 09-04-2002, 08:07 PM

The only evolutionary explaination I've heard of is that menopause allows for women to start paying attention to their grandchildren instead of having more children. This probably has something to do with the historical constrait that women only have a finite number of chances (eggs) to reproduce.

scigirl · 09-04-2002, 08:12 PM

My guess - evolution didn't evolve this feature, it's some by-product of us living longer than we are supposed to.

scigirl

NOTE: supposed to according to natural selection, not human moral standards! I love the elderly and may in fact work with them someday!!

scigirl · 09-04-2002, 08:19 PM

Well here's what pubmed has to say:

<a href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=118919 33&dopt=Abstract" target="_blank">Antiquity of postreproductive life: are there modern impacts on hunter-gatherer postreproductive life spans?</a>

Quote:

Female postreproductive life is a striking feature of human life history and there have been several recent attempts to account for its evolution. But archaeologists estimate that in the past, few individuals lived many postreproductive years. Is postreproductive life a phenotypic outcome of modern conditions, needing no evolutionary account? This article assesses effects of the modern world on hunter-gatherer adult mortality, with special reference to the Hadza. Evidence suggests that such effects are not sufficient to deny the existence of substantial life expectancy at the end of the childbearing career. Data from contemporary hunter-gatherers (Ache, !Kung, Hadza) match longevity extrapolated from regressions of lifespan on body and brain weight. Twenty or so vigorous years between the end of reproduction and the onset of significant senescence does require an explanation.

This article seems to say that my above statement is incorrect, and that it has to have some sort of explanation.

<a href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=114002 15&dopt=Abstract" target="_blank">A critique of the grandmother hypotheses: old and new.</a>

Quote:

The singularity of reproductive senescence in human females has led many investigators to consider menopause an adaptation permitting increased maternal investment in existing progeny. Much of the focus has been on the grandmother hypothesis-the notion that aging women gain an inclusive fitness advantage from investing in their grandchildren. This hypothesis has evolved from an explanation for menopause into an explanation for the exceptionally long postreproductive lifespan in human females. In the old grandmother hypothesis, menopause is an adaptation facilitating grandmothering; it is about stopping early in order to create a postreproductive lifespan. In the new grandmother hypothesis, grandmothering is an adaptation facilitating increased longevity, and menopause is a byproduct. This paper reviews and critically evaluates the evidence for and against both hypotheses, focusing on key predictions of each. If menopause is the result of selection for increased maternal investment, this involved mainly mothers, not grandmothers.

From what I can tell, nobody really knows why menopause evolved. Interesting question. . .

scigirl

scigirl · 09-04-2002, 08:22 PM

Here's another one:

<a href="http://http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=113933 31&dopt=Abstract" target="_blank">The evolution of menopause and human life span.</a>

Quote:

Noteworthy data is emerging to support the existence of longevity-enabling genes. Our observations of the relationship between reproductive fitness and longevity among centenarians support theories that posit strong selective forces in the determination of how fast humans age and their susceptibility to diseases associated with ageing. Current data support the idea that there is no selective advantage for humans to have a lifespan of approximately 100 years. Rather, getting to such a very old age may be a by-product of longevity-enabling genes that maximize the length of time during which women can bear children, and during which they can increase the survival probabilities of their children and grandchildren. We thus review the literature pertaining to the relationship between reproductive fitness and longevity.

<a href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=112238 85&dopt=Abstract" target="_blank">Evolution of the human menopause.</a>

Quote:

Menopause is an evolutionary puzzle since an early end to reproduction seems contrary to maximising Darwinian fitness. Several theories have been proposed to explain why menopause might have evolved, all based on unusual aspects of the human life history. One theory is that menopause follows from the extreme altriciality of human babies, coupled with the difficulty in giving birth due to the large neonatal brain size and the growing risk of child-bearing at older ages. There may be little advantage for an older mother in running the increased risk of a further pregnancy when existing offspring depend critically on her survival. An alternative theory is that within kin groups menopause enhances fitness by producing post-reproductive grandmothers who can assist their adult daughters. Such theories need careful quantitative assessment to see whether the fitness benefits are sufficient to outweigh the costs, particularly in circumstances of relatively high background mortality typical of ancestral environments. We show that individual theories fail this test, but that a combined model incorporating both hypotheses can explain why menopause may have evolved.

scigirl

Jesus Tap-Dancin' Christ · 09-04-2002, 09:44 PM

And I have found a refutation of creation. I'll let you think about why menopause spells doom for biblical literalists--I have to go to bed for 8 am class.

pug846 · 09-05-2002, 10:53 AM

Okay, thanks for the responses.

09-04-2002, 07:58 PM	#1
pug846 Veteran Member Join Date: Mar 2001 Location: Somewhere Posts: 1,587	Question Forgive my ignorance, but how did menopause, evolve? It doesn�t seem that something that comes along so late in life would be susceptible to selection pressures. I�m also under the impression that humans are the only animals that go through something like menopause. Is there any reason for this? Why did it come into play so late in our evolutionary history? [ September 04, 2002: Message edited by: pug846 ]</p>

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09-04-2002, 08:03 PM	#2
Max Bane Junior Member Join Date: Dec 2001 Location: Wisconsin, USA Posts: 51	Argh, his edit was too fast for me. [ September 04, 2002: Message edited by: Max Bane ]</p>

09-04-2002, 08:07 PM	#4
RufusAtticus Veteran Member Join Date: Nov 2001 Location: NCSU Posts: 5,853	The only evolutionary explaination I've heard of is that menopause allows for women to start paying attention to their grandchildren instead of having more children. This probably has something to do with the historical constrait that women only have a finite number of chances (eggs) to reproduce.

09-04-2002, 08:12 PM	#5
scigirl Veteran Member Join Date: Jul 2001 Location: Seattle Posts: 4,261	My guess - evolution didn't evolve this feature, it's some by-product of us living longer than we are supposed to. scigirl NOTE: supposed to according to natural selection, not human moral standards! I love the elderly and may in fact work with them someday!!

09-04-2002, 09:44 PM	#8
Jesus Tap-Dancin' Christ Veteran Member Join Date: Apr 2001 Location: Heaven Posts: 6,980	And I have found a refutation of creation. I'll let you think about why menopause spells doom for biblical literalists--I have to go to bed for 8 am class.

09-05-2002, 10:53 AM	#9
pug846 Veteran Member Join Date: Mar 2001 Location: Somewhere Posts: 1,587	Okay, thanks for the responses.

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